The present invention relates to a biotissue excising instrument used to excise biotissue using, for example, a high-frequency current.
A high-frequency snare has hitherto been known as biotissue excising instrument used to excise biotissue using a high-frequency current. The high-frequency snare is, for example, composed of a sheath 100 inserted endoscopically into a coelom through, for example, a treatment instrument insertion channel in an endoscope, a manipulation portion 102 provided at a proximal end of the sheath 100, a manipulation wire 104 inserted into the sheath 100 from the manipulation portion 102, and a slider 106 provided in the manipulation portion 102 to manipulate the manipulation wire 104 so as to advance and retreat freely, as shown in FIG. 26.
The manipulation wire 104 has a snare wire 110 at its leading end portion as a treatment portion that freely projects out of and sinks into an opening 100a in the leading end of the sheath 100. The snare wire 110 is shaped like a loop. It unfolds owing to its own recovery force when projected out of the opening 100a in the leading end of the sheath 100 when the slider 106 slides forward as shown in FIG. 26. Further, the snare wire 110 is compressed to reduce its own diameter when the slider 106 is slid toward an operator to pull part of the snare wire 110 into the sheath 100 via the manipulation wire 104 as shown in FIG. 27.
Accordingly, to excise biotissue, for example, a polyp using a high-frequency snare configured as described above, the snare wire 110 projected out of the opening 100a in the leading end of the sheath 100 and then unfolded is first caught on the polyp A as shown in FIG. 28A. Subsequently, in this caught state, the manipulation wire 104 is pulled toward the operator (the slider 106 is slid toward the operator) to reduce the diameter of the snare wire 110 as shown in FIG. 28B. Thus, the polyp A is bound tightly. In this tightly bound state, a high-frequency current is passed through the snare wire 110 to excise the polyp A.
All conventional high-frequency snares are of a frontward projecting type in which the snare wire 110 projects out of the opening 100a in the leading end of the sheath 100. Thus, when biotissue is excised using only this forward-projecting type of high-frequency snare, several problems may occur as described below.
That is, with the forward projecting type high-frequency snare, the snare wire 110 is continuously contracted by the inner surface of the sheath 100 until the snare wire 110 projects out of the opening 100a in the leading end of the sheath 100. Thus, the snare wire 100 is not opened until it is projected out of the opening 100a in the leading end of the sheath 100 by a certain distance by sliding the slider 106 of the manipulation portion 102 forward by a predetermined stroke. That is, with the forward projecting type high-frequency snare, the stroke of the slider 106 of the manipulation portion 102 cannot be used efficiently for the operation of increasing the diameter of the snare wire 110. Thus, the snare wire 110 cannot be linearly unfolded according to the stroke of the slider 106.
Further, with the forward projecting type high-frequency snare, the snare wire 100 must be unfolded with the leading end of the sheath 100 located in front of the polyp A and then allowed to approach the polyp A from above it so that the loop portion of the snare wire 100 is caught on the polyp A as shown in FIGS. 29A and 29B. However, the polyp A formed in the body does not always accommodate such an approach. It may be difficult to excise the polyp using the forward projecting type high-frequency snare depending on the manner of formation of the polyp.
Furthermore, with the forward projecting type high-frequency snare, rotation of the sheath 100 only causes the snare wire 100 to rotate around the axis of the sheath 100. Thus, in spite a change in the direction in which the loop is opened, the position of the snare wire 110 is not changed. Consequently, if the polyp A is located, for example, at the side of the snare wire 110 and it is difficult to allow the snare wire to approach the polyp A (direct the opening 100a in the leading end of the sheath 100 toward the polyp A), then the snare wire 110 cannot be caught on the polyp A. Therefore, it may be virtually impossible to carry out excision using the snare wire 110.